1. Field of the Invention
The present invention relates to a sintered alloy which is suitable for a turbo component for turbocharger, particularly a nozzle body and the like which require heat resistance, corrosion-resistance and wear-resistance, and a method for manufacturing the sintered alloy.
2. Background of the Invention
Generally, in a turbocharger provided in an internal combustion engine, a turbine is rotatably supported by a turbine housing connected with an exhaust manifold of the internal combustion engine and a plurality of nozzle vanes are rotatably supported so as to surround the periphery of the turbine. An exhaust gas flowed in the turbine housing is flowed in the turbine from the outside thereof and emitted in the axial direction thereof while the turbine is rotated. Then, air to be supplied into the internal combustion engine is compressed by the rotation of an air compressor which is provided at the same shaft in the opposite side of the turbine.
Here, the nozzle vanes are rotatably supported by a ring-shaped component called as a “nozzle body” or “mount nozzle”. The shaft of the nozzle vanes is passed through the nozzle body and connected with a link mechanism. Then, the nozzle vanes are rotated by driving the link mechanism so that the degree of opening of the inflow path of the exhaust gas is controlled. The present invention is directed at a turbo component such as the nozzle body (mount nozzle) or plate nozzle to be attached thereto which is to be provided in the turbine housing.
The aforementioned turbo component for turbocharger requires heat resistance and corrosion resistance because the turbo component is contacted with high temperature corrosion gas and requires wear resistance because the turbo component is slid relative to the nozzle vanes. In this point of view, conventionally, high chrome cast steel, wear-resistant material made of JIS (Japanese Industrial Standards) SCH22 to which chrome surface treatment is conducted for the enhancement of corrosion resistance and the like are used. Moreover, as an inexpensive wear-resistant component having heat resistance, corrosion resistance and wear resistance is proposed a wear-resistant sintered component in which carbides are dispersed in the base material of a ferric steel material (Refer to Patent document No. 1).
However, since the sintered component disclosed in Patent document No. 1 is formed through liquid phase-sintering, the sintered component may be machined as the case of severe dimensional accuracy. Since the large amount of hard carbides are precipitated in the sintered component, the machinability of the sintered component is not good and thus required to be improved. Moreover, the turbo component is normally made of austenitic heat-resistant material, but the turbo component disclosed in Patent document No. 1 is made of ferritic stainless material. In this case, since the thermal expansion coefficient of the turbo component is different from those of the adjacent components, some spaces are formed between the turbo component and the adjacent components, causing the insufficient connections between the turbo component and the adjacent components and rendering component design available in the turbocharger difficult. It is therefore desired that the turbo component has a similar thermal expansion coefficient to those of the adjacent components made of austenitic heat-resistant material.
Patent document No. 1: JP-B2 No. 3784003 (Patent)